Abstract

The principal aims of the present study were to examine diel feeding and feedingentrainablelocomotor activity rhythms in cultured greenback flounderRhombosolea tapirina (Gunther 1862) and to examine their applications to theculture of the species.A computerised tank-based waste pellet monitoring system was developed andused to study feeding rhythms in greenback flounder. It consisted of an infraredsensor and a recording unit capable of continuously detecting wastage withreference to time. Actual feed intake was determined as the difference betweenpellets presented by a mechanical belt feeder and the uneaten pellets detected bythe monitoring system. Diel feeding rhythms were described by the temporalvariation of actual feed intake at intervals of 30 mm.The role of light-dark (LD) cycles and food deprivation in the regulation of dielfeeding rhythms in greenback flounder (75-281 g) was examined. The fish is adiurnal feeder, but is capable of feeding at night. Feeding appeared to have anendogenous circadian component. A LD 12:12 cycle was a potent environmentalcue to entrain circadian feeding rhythms. Re-feeding after a single period of fooddeprivation of 26-57 h was capable of temporarily over-riding feeding rhythms. The effect of feeding regime (difference in temporal distribution of feed) ongrowth and proximate body composition was investigated. The feeding regimeshad an impact on the growth, with 1 meal of 3 h during the scotophase resulting inlower growth than the other five feeding regimes (feed continuously available, 12meals of 1 h per meal, 6 meals of 1 h per meal, 3 meals of 2 h per meal, and 1meal of 3 h during the photophase). However, the feeding regimes did notsignificantly influence proximate body composition.Locomotor activity patterns were examined in relation to feeding regimes andcombinations of meal size and meal duration at a single daily meal. Groups assigned to a higher frequency (and hence a longer total duration) of daily mealswere less active during mealtime even though the daily ration was equivalent aspercentage of body weight per day. A distinct food anticipatory activity (FAA)was observed in the groups of fish receiving a single daily meal either duringphotophase or during scotophase, and FAA also developed before at least one outof three daily meals but not before any meal in the regimes of six daily meals ormore than six daily meals.It was further demonstrated that whether or not a single daily meal is a potentzeitgeber to synchronise daily locomotor activity pattern depends on thecombination of meal size and meal duration. The fish fed at the meal sizes of 0.25and 0.5% BW day' exhibited FAA under all the three meal durations (1, 3 and 7h) investigated. FAA was also expressed by the fish fed at 1.5% BW day' butonly combined with the meal duration of 1 h. But, weight loss is not essential forthe fish to develop FAA. At each meal size, the group assigned to the 7 h mealhad lower and shorter FAA than that assigned to the 3 h meal, which in turn hadlower values than that assigned to the 1 h meal. There was a positive correlationbetween the mean durations of FAA and post-feeding activity (r = 0.87; P < 0.01;n = 7). The results suggest that the greenback flounder is capable of responding tothe energetic (meal size) and temporal (meal duration) impacts of a single dailymeal. The latency of FAA was about 21 days. FAA persisted up to three daysduring food deprivation, indicating that FAA may be mediated by a feedingentrainablecircadian oscillator. The present study is one of only a few investigating diel feeding rhythms,feeding-entrainable locomotor activity rhythms and effects of temporaldistribution of feed on growth performance in cultured flatfish. The finding thatmagnitude and duration of FAA in greenback flounder were influenced by mealsize and meal duration of a single daily meal is perhaps the first obtained for fish,and may have implications for the elucidation of the feeding entrainmentpathways which remain unknown for all animals.